Mr Nielsen later went to Madsen's lab while he was looking for his girlfriend and met the inventor's wife, who expressed surprise when she was told someone else was supposed to be with her husband on the submarine.

Madsen admits dismembering her body and throwing it overboard, but denies the charge of premeditated murder.

The accused says the 30-year-old freelance journalist died when the air pressure suddenly dropped and toxic fumes filled his homemade submarine, while he was up on deck.

A cause of death has not been discerned.

The medical examiner told the court on Thursday that the effect of being exposed to water and a period of decomposition makes it difficult to determine if carbon monoxide or the cutting of Ms Wall's throat was what caused her to die.

What we know about submarine murder

Ms Wall's torso was found with more than 38 stab wounds and lesions.

On Wednesday, Madsen claimed he slashed her body to prevent the build-up of gases that occurs when a person dies.

The examiner contradicted Madsen's statement, saying the stab lesions were "superficial" and as a result "serve no purpose of letting gasses leave or enter."

Giving evidence on other wounds inflicted on Ms Wall, the examiner said lesions inside Ms Wall's genitals "could" have been inflicted while she was dying, but the 15 punctures above her genitals were most likely inflicted after her death.

The prosecution have painted a picture of Madsen as a sexual sadist who was obsessed with beheadings and murdered Ms Wall as part of a sexual fantasy.

The examiner also told the court the victim's head may have been restrained or gagged and that her hands and feet could have been tied.

Ms Wall's torso showed evidence of blunt force being inflicted while she was still alive, she added.

"This typically happens if you run into a table or is hit by a hand or another body part," the medical examiner told the court.

A witness who helped rescue Madsen from the sinking submarine told the court on Thursday that the accused seemed "calm and focused and not as shaken, other than [a] small shiver".

Ms Wall's boyfriend added about his late girlfriend: "She was at the same time an incredibly ambitious journalist and an amazingly curious person, who found beauty in all places and couldn't stop herself from travelling, experiencing, discovering and sharing with others."

Court hears disturbing details of Kim Wall's death

Madsen has admitted lying to investigators and changing his account of what actually happened to Ms Wall several times.

The prosecution has said it will seek a life sentence, which in Denmark averages around 16 years, or safe custody, a legal alternative which would keep him behind bars indefinitely as long as he is deemed dangerous.

Six out of 37 experts and witnesses have been heard so far in the trial, which continues on Friday.